[PATCH v2 1/2] kexec: Introduce "/sys/kernel/kexec_crash_low_size"

[Xunlei Pang]

"/sys/kernel/kexec_crash_size" only handles crashk_res, it
is fine in most cases, but sometimes we have crashk_low_res.
For example, when "crashkernel=size[KMG],high" combined with
"crashkernel=size[KMG],low" is used for 64-bit x86.

Like crashk_res, we introduce the corresponding sysfs file
"/sys/kernel/kexec_crash_low_size" for crashk_low_res.

So, the exact total reserved memory is the sum of the two.

crashk_low_res can also be shrunk via this new interface,
and users should be aware of what they are doing.

Suggested-by: Dave Young <dyoung@xxxxxxxxxx>
Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxx>
---
 include/linux/kexec.h |  4 ++--
 kernel/kexec_core.c   | 23 ++++++++++++-----------
 kernel/ksysfs.c       | 25 +++++++++++++++++++++++--
 3 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index d743777..4f271fc 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -304,8 +304,8 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
 int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
 		unsigned long long *crash_size, unsigned long long *crash_base);
-int crash_shrink_memory(unsigned long new_size);
-size_t crash_get_memory_size(void);
+int crash_shrink_memory(struct resource *res, unsigned long new_size);
+size_t crash_get_memory_size(struct resource *res);
 void crash_free_reserved_phys_range(unsigned long begin, unsigned long end);
 
 int __weak arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 5616755..707d18e 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -925,13 +925,13 @@ void crash_kexec(struct pt_regs *regs)
 	}
 }
 
-size_t crash_get_memory_size(void)
+size_t crash_get_memory_size(struct resource *res)
 {
 	size_t size = 0;
 
 	mutex_lock(&kexec_mutex);
-	if (crashk_res.end != crashk_res.start)
-		size = resource_size(&crashk_res);
+	if (res->end != res->start)
+		size = resource_size(res);
 	mutex_unlock(&kexec_mutex);
 	return size;
 }
@@ -945,7 +945,7 @@ void __weak crash_free_reserved_phys_range(unsigned long begin,
 		free_reserved_page(boot_pfn_to_page(addr >> PAGE_SHIFT));
 }
 
-int crash_shrink_memory(unsigned long new_size)
+int crash_shrink_memory(struct resource *res, unsigned long new_size)
 {
 	int ret = 0;
 	unsigned long start, end;
@@ -958,8 +958,9 @@ int crash_shrink_memory(unsigned long new_size)
 		ret = -ENOENT;
 		goto unlock;
 	}
-	start = crashk_res.start;
-	end = crashk_res.end;
+
+	start = res->start;
+	end = res->end;
 	old_size = (end == 0) ? 0 : end - start + 1;
 	if (new_size >= old_size) {
 		ret = (new_size == old_size) ? 0 : -EINVAL;
@@ -975,17 +976,17 @@ int crash_shrink_memory(unsigned long new_size)
 	start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
 	end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
 
-	crash_free_reserved_phys_range(end, crashk_res.end);
+	crash_free_reserved_phys_range(end, res->end);
 
-	if ((start == end) && (crashk_res.parent != NULL))
-		release_resource(&crashk_res);
+	if ((start == end) && (res->parent != NULL))
+		release_resource(res);
 
 	ram_res->start = end;
-	ram_res->end = crashk_res.end;
+	ram_res->end = res->end;
 	ram_res->flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM;
 	ram_res->name = "System RAM";
 
-	crashk_res.end = end - 1;
+	res->end = end - 1;
 
 	insert_resource(&iomem_resource, ram_res);
 
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index ee1bc1b..3336fd5 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -105,10 +105,30 @@ static ssize_t kexec_crash_loaded_show(struct kobject *kobj,
 }
 KERNEL_ATTR_RO(kexec_crash_loaded);
 
+static ssize_t kexec_crash_low_size_show(struct kobject *kobj,
+				       struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "%zu\n", crash_get_memory_size(&crashk_low_res));
+}
+static ssize_t kexec_crash_low_size_store(struct kobject *kobj,
+				   struct kobj_attribute *attr,
+				   const char *buf, size_t count)
+{
+	unsigned long cnt;
+	int ret;
+
+	if (kstrtoul(buf, 0, &cnt))
+		return -EINVAL;
+
+	ret = crash_shrink_memory(&crashk_low_res, cnt);
+	return ret < 0 ? ret : count;
+}
+KERNEL_ATTR_RW(kexec_crash_low_size);
+
 static ssize_t kexec_crash_size_show(struct kobject *kobj,
 				       struct kobj_attribute *attr, char *buf)
 {
-	return sprintf(buf, "%zu\n", crash_get_memory_size());
+	return sprintf(buf, "%zu\n", crash_get_memory_size(&crashk_res));
 }
 static ssize_t kexec_crash_size_store(struct kobject *kobj,
 				   struct kobj_attribute *attr,
@@ -120,7 +140,7 @@ static ssize_t kexec_crash_size_store(struct kobject *kobj,
 	if (kstrtoul(buf, 0, &cnt))
 		return -EINVAL;
 
-	ret = crash_shrink_memory(cnt);
+	ret = crash_shrink_memory(&crashk_res, cnt);
 	return ret < 0 ? ret : count;
 }
 KERNEL_ATTR_RW(kexec_crash_size);
@@ -218,6 +238,7 @@ static struct attribute * kernel_attrs[] = {
 #ifdef CONFIG_KEXEC_CORE
 	&kexec_loaded_attr.attr,
 	&kexec_crash_loaded_attr.attr,
+	&kexec_crash_low_size_attr.attr,
 	&kexec_crash_size_attr.attr,
 	&vmcoreinfo_attr.attr,
 #endif
-- 
1.8.3.1